A silicon wafer to be used for a semiconductor device is produced from an ingot of silicon single crystal grown by the Czochralski method or the like. In general, the single crystal ingot is processed into a cylindrical form in an outer periphery grinding step, and sliced into a disk-like blank wafer in a slicing step. The blank wafer is then finished to have a specific diameter in a chamfering step by chamfering the periphery thereof; the parallelism of surfaces is adjusted in a rough polishing (lapping) step by polishing opposite surfaces thereof; the resulting wafer is subjected to chemically remove processing strain/distortion in an etching step; and it is finally finished into a mirror surface with high flatness in a mirror polishing (polishing) step by means of mechanochemical polishing using a polishing agent such as a colloidal silica solution. The silicon wafer after the mirror polishing is cleaned in a washing step to remove foreign substances such as particles or metals remaining on the surface thereof.
In the washing step, for example, as shown in Patent Literature 1, the wafer surface is washed by performing an ozone water treatment that oxidizes the wafer surface by use of ozone water, and a diluted hydrofluoric acid treatment that removes an oxide film on the wafer surface by use of a diluted hydrofluoric acid (a diluted aqueous solution of hydrogen fluoride) or alternately repeating these treatments as occasion demands. Thereafter, the resulting wafer is subjected to a pure water treatment using pure water, and finally to a spin drying treatment.
The silicon wafer for which the cleaning is completed is often subjected to a special treatment to adjust the properties of the surface or the surface vicinity thereof according to the intended use of a semiconductor device to which the silicon wafer is applied. The most well-known one among such special treatments is an epitaxial treatment for vapor-depositing an epitaxial layer on the surface of the silicon wafer for production of an epitaxial wafer having the epitaxial layer formed on the silicon wafer surface. The epitaxial wafer is high in crystal integrity, and is frequently used for a highly-integrated semiconductor device because of excellent characteristics thereof.
In recent years, minute convex defects on the silicon wafer surface which could not be detected in the past have been recognized as a problem as the defect detectability is remarkably improved in association with the progress of inspection equipment and technology. Such convex defects can be detected using a wafer surface defect inspection equipment (e.g., MAGICS by Lasertec Corporation, Surfscan SP2 by KLA-Tencor Corporation), and appear in a dot-like or linear shape.
It has been revealed that such minute convex defects are generated during the mirror polishing step, and they are called PIDs (Polishing Induced Defects). Many of the PIDs remain without being removed in the cleaning process and induce, during the formation of the epitaxial layer, convex defects on the surface of the epitaxial wafer.
A method for finish-polishing a silicon wafer is described in Patent Literature 2, wherein the polishing rate in finish polishing on the final stage of the mirror polishing step is set to 10 nm/min or less. This finish-polishing method can suppress generation of PIDs by limiting the polishing rate.